Oil-free fluid machine having two or more rotors

ABSTRACT

An oil-free fluid machine unit is provided of which the fluid machine has two or more rotors and torque transmission between the rotors can be performed without a need of using lubrication oil thereby eliminating contamination induced by lubrication oil and without reduction of longevity of the synchronizing gears. The drive shaft  12  of the drive motor  11  is connected to the rotor shaft  14  of the fluid machine, synchronization gears  18  and  19  are attached to the rotor shafts  14  and  15  at the motor  11  side end of the rotor shafts respectively, and pulleys  16  and  17  are attached to the rotor shafts  14  and  15  at the other side ends respectively opposite to the motor  11  and a belt is looped over the pulleys so that the pulleys are rotated in counter direction to each other. At least one of the synchronization gears is made of plastic material. Thus, torque transmission between the rotors is done in two ways, via synchronization gear drive and belt drive.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to oil-free fluid machines having two or more rotors, specifically to dry-sealed mechanical vacuum pumps such as Roots type, screw type, and claw type vacuum pumps having two or more rotors which are rotated in synchronism with one another to perform well-balanced torque transmission without a need for lubrication oil for lubricating the drive mechanism of the rotors thereby eliminating occurrence of oil contamination.

2. Description of the Related Art

Fluid machines having two or more counter-rotating meshed lobed rotors accommodated in a rotor casing to expel air trapped in a space between the wall of the casing and the rotor surface by rotating the rotors in synchronization with one another are widely used as vacuum pumps such as roots vacuum pumps, claw vacuum pumps, and screw vacuum pumps.

In these dry mechanical vacuum pumps having two or more lobed rotors, synchronization gears made of metal is usually adapted to allow meshing lobed rotors to rotate in directions opposite to each other. The synchronization gears made of metal are needed to be lubricated with oil, grease, or a solid lubricant, etc. Further, noise occurs due to contact meshing of the synchronization gears.

Lubrication of the synchronization gears is performed with oil, grease, or a solid lubricant, etc. Oil lubrication deteriorates quality of vacuum. In a case of low rotation speed of the rotors, grease may be used, but refilling of grease is not easy. Solid lubricants are not adequate when the gears experience large loads. Grease is poor in friction heat removing performance, and solid lubricants can not remove friction heat.

In a case lubricating oil is reserved in a gear case and supplied to where needed when operating the vacuum pump, there are problems that oil leaks through oil seals of drive shafts of the rotors. Particularly, oil molecules leaked to the pump chamber defuse into the vessel to be evacuated and deteriorate quality of vacuum.

To deal with the problems, it is thinkable to use plastic gears or toothed belt (synchronous belt) in order to transmit driving force without lubrication. However, there is a disadvantage that large torque can not be transmitted, since the plastic gears and toothed belt are lower in strength as compared with metal gears, resulting in decreased operation life.

In Japanese Laid-Open Patent Application No. 6-185483 (Patent literature 1) is disclosed a dry mechanical vacuum pump of roots type, in which an annular magnet is attached to an end of the drive shaft of a drive motor and to an end of one of the rotary shaft respectively, and a partition member made of electrical insulating material is provided to run in the gap between the outer periphery and inner periphery of the annular magnets so that the pump body side where the annular magnet attached to the rotary shaft exists is separated from the outside of the pump body where the annular magnet attached to the drive shaft of the motor exists. Synchronization gears consisting of a metal gear and a plastic gear for allowing the two rotors to rotate in direction opposite to each other in synchronization with each other are provided at the other ends of the rotary shafts respectively. With this construction, lubricating oil for lubricating the synchronization gears is not needed, oil seals for preventing oil leak from the gear chamber to the pump chamber and for preventing oil leak from the gear chamber to outside are eliminated, and power loss due friction is decreased.

However, with the dry mechanical vacuum pump of roots type disclosed in the patent literature 1, driving torque of the drive motor is transmitted via the annular magnets to one of the rotor and this driving torque is transmitted to the other rotor by way of the synchronization gears consisting of the metal gear and plastic gear. Therefore, when increased driving torque is transmitted from the drive motor to one of the rotors, all of the driving torque is transmitted to the other rotor by way of the synchronization gears and the plastic gear may be fractured or is decreased in operation life due to the increased torque.

SUMMARY OF THE INVENTION

Therefore, it is the object of the invention to provide an oil-free fluid machine unit with which torque transmission can be performed between two or more rotors in synchronized counter-rotation with one another without need for lubrication oil thereby eliminating contamination induced lubrication oil and without reduction of operation life of synchronization gears of the fluid machine.

To attain the object, the present invention proposes an oil-free fluid machine unit including an oil-free fluid machine, a motor connected to one of rotor shafts of the fluid machine, and a mounting base for mounting the fluid machine and the motor, the fluid machine having a rotor casing and two or more lobed rotors accommodated in the rotor casing rotatably to expel gas trapped in pockets formed between the lobes and the rotor casing as the rotors rotate, in which a pulley is attached to each of said rotor shafts at an end opposite to the motor side end thereof, a belt being looped over pulleys attached to adjacent rotor shafts so that pulleys attached to adjacent rotor shafts are rotated in counter direction to each other; and synchronization gears are attached to the other ends of the rotor shafts respectively, at least one of the synchronization gears being made of plastic material; thereby enabling torque transmission between the rotors in two ways, via belt driving and via synchronization gear drive.

By composing the oil-free fluid machine unit such that torque transmission between the rotors is carried out in two ways, via belt drive and via synchronization gear drive, load torque exerting on the synchronization gears is reduced. Therefore, by making at least on of the synchronization gears of plastic material, the use of lubrication oil for lubricating the synchronization gears becomes unnecessary. Further, as only a part of torque transmitted between adjacent rotors is transmitted via the belt, total torque transmission capacity can be increased with load torque exerting on the synchronization gears reduced. Thus, by adopting a plastic gear in the drive transmission mechanism composed like this, problems of reduced torque transmission capacity by use of plastic gears and poor endurance against mechanical load of plastic gears can be solved together.

By providing the synchronization gears at the motor side and the pulleys at the opposite side which is open to outside, torque transmission between the rotors is performed at both end sides of the rotors, and well-balanced torque transmission is carried out, and further the belt can be replaced easily when it has worn. Therefore, by adopting the drive transmission mechanism in an oil-free fluid machine, contamination with lubricating oil can be eliminated, and particularly a dry mechanical vacuum pump of high efficiency which can produce oil-free vacuum can be provided.

It is preferable that an idler pulley is provided to allow pulleys attached to adjacent rotor shafts respectively to be rotated in counter direction to each other by looping a belt over the adjacent pulleys via the idler pulley.

As has been described in the foregoing, torque transmission between the rotors is carried out in two ways, via synchronization gear drive and via belt drive, load torque exerting on the synchronization gears is reduced, and plastic gear or gears can be adopted for the synchronization gears, resulting in requiring no lubricant to lubricate the synchronization gears and prolonged operation life of the synchronization gears. Therefore, by adopting the drive transmission mechanism in an oil-free fluid machine, contamination with lubricating oil can be eliminated, and particularly a dry mechanical vacuum pump unit of high efficiency which can produce oil-free vacuum can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a plan view of the oil-free fluid machine composed as a dry mechanical vacuum pump of roots type equipped with the drive transmission mechanism according to the present invention, FIG. 1B is a front view thereof, and FIG. 1C is a side view thereof.

FIG. 2A is a sectional view along line A-A in FIG. 1A, and FIG. 2B is a cross sectional view along Line C-C in FIG. 1A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of the present invention will now be detailed with reference to the accompanying drawings. It is intended, however, that unless particularly specified, dimensions, materials, relative positions and so forth of the constituent parts in the embodiments shall be interpreted as illustrative only not as limitative of the scope of the present invention.

FIG. 1A is a plan view of the oil-free fluid machine composed as a dry mechanical vacuum pump of roots type equipped with the drive transmission mechanism according to the present invention, FIG. 1B is a side view thereof, and FIG. 1C is a front view thereof. FIG. 2 A is a sectional view along line A-A in FIG. 1A, and FIG. 2B is a cross sectional view along Line C-C in FIG. 1A.

Although the invention will be explained taking up as an example a dry mechanical vacuum roots pump of two rotors equipped with the drive transmission mechanism, the drive transmission mechanism applied to the fluid machine of the invention can be applied to any of fluid machines having two or more counter-rotating meshed lobed rotors accommodated in a rotor casing parallel to one another to be rotated in synchronization with one another and torque transmission between the rotors is performed unlubricated condition, so applicable also to screw vacuum pumps and claw vacuum pumps.

Referring to FIGS. 1-2, reference numeral 10 is a dry mechanical vacuum roots pump, 11 is a drive motor for driving the vacuum pump 10, 12 is a driving shaft of the drive motor 11. Reference numeral 13 is a coupling for connecting the driving shaft 12 of the drive motor 11 to an end of a rotor shaft 14 of the vacuum pump, 15 is the other rotor shaft. Reference numeral 16 and 17 are pulleys over which a belt 26 is looped to transmit torque transmitted to the rotor shaft 14 to another rotor shaft 15. Reference numerals 18 and 19 are synchronization gears attached to the other end of the rotor shafts 14 and 15 respectively meshing with each other to allow synchronized rotation of the rotor shafts 14 and 15 in direction opposite to each other. Reference numeral 20 is a mounting base for supporting the vacuum pump 10 and the drive motor 11. Reference numerals 21 and 22 are fixing means for fixing the vacuum pump 10 and the drive motor 11 to the mounting base 20. Reference numerals 27 and 28 (see FIG. 2B) are an outlet port and intake port respectively.

As shown in FIG. 2B, a pair of three-lobes roots type rotors 102 and 103 are accommodated in a pump chamber 101 of a rotor casing 100. The rotors 102 and 103 are integrated respectively with the rotary shafts 14 and 15 which are supported by oilless bearings not shown in the drawings. The rotors 102 and 103 can be rotated without contact between lobe surfaces thereof and also without contact between the peripheries of the lobes and the wall surface of the pump chamber 101.

Fluid such as air is trapped in pockets 104 surrounding the lobes and carried from the intake port 28 side to the outlet port 27 side and expelled from there as the rotors 102 and 103 rotate as shown by arrows 29 in FIG. 2B.

Returning to FIGS. 1A, B, C, the vacuum pump 10 is fixed to the mounting base 20 by means of the fixing means 21, and the driving shaft 12 of the motor 11 also fixed to the mounting base 20 is connected to the rotary shaft 14 by means of the coupling 13. The synchronization gear 18 is attached to the rotor shaft 14 at the motor 11 side end thereof as shown in FIG. 2A, and to the other end side of the rotor shaft 14 is attached the pulley 16 as shown in FIG. 1B.

The synchronization gear 19 is attached to the rotor shaft 15 at the motor 11 side end thereof, and to the other end side of the rotor shaft 14 is attached the pulley 17. The belt 26 is looped over the pulleys 16 and 17 via an idle pulley 25 so that the rotor shaft 14 and 15 rotate in counter direction to each other.

At least one of the synchronization gears 18 and 19 is made of plastics, and the other gear is made of plastics or metal. By using the plastic gear, lubricant for lubricating the meshing gears can be dispensed with. Synchronized rotation of the rotors 14, 15 is secured by the synchronization gears 18 and 19. Torque transmission between the rotors is done in two ways, via the pulleys 16 and 17 and via the synchronization gears 18 and 19. For example, about 70% of torque is transmitted via the pulleys 16 and 17 and about 30% of torque is transmitted via the synchronization gears 18 and 19.

By composing the drive transmission mechanism in the oil-free fluid machine like this, torque is transmit from the rotor shaft 14 connected to the motor 11 to the rotor shaft 15 in two ways, via the synchronization gears 18, 19 and via the pulleys 17, 16. Therefore, torque transmitted via the synchronization gears 18, 19 is reduced. So, making at least of one of the synchronization gears 18 and 19, the use of lubrication oil can be eliminated. Further, as torque load on the synchronization gears is reduced, operation life of the plastic gear is increased. Thus, problems of reduced torque transmission capacity by use of plastic gears and poor endurance against mechanical load of plastic gears can be solved together.

By applying the drive transmission mechanism to an oil-free fluid machine, oil contamination induced by lubrication oil leak is eliminated. Further, by providing the pulleys 16 and 17 in a side opposite to the motor 11 side, replacement of the belt is facilitated when it is deteriorated.

As has been described in the foregoing, by composing the drive transmission mechanism to transmit torque from a rotor shaft 14 to a rotor shaft 15 such that synchronization gears 18, 19 are attached to the rotor shafts 14, 15 respectively at an end side thereof and pulleys 16, 17 are attached to the other end side respectively with a belt 26 looping over the pulleys 16, 17 via a idler pulley 25 so that the pulleys rotate in counter direction to each other, a part of torque transmission is done via the synchronization gears 18, 19 and the remaining torque transmission is done via the pulleys 16, 17. Therefore, load torque exerting on the synchronization gears is reduced, and plastic gear or gears can be adopted for the synchronization gears, resulting in requiring no lubricant to lubricate the synchronization gears and in prolonged operation life of the synchronization gears.

Therefore, by adopting the drive transmission mechanism in an oil-free fluid machine, contamination with lubricating oil can be eliminated, and particularly a dry mechanical vacuum pump of high efficiency which can produce oil-free vacuum can be provided.

According to the invention, drive transmission mechanism increased in torque transmission capacity and longevity without a need of using lubrication oil is provided, and by adopting the drive transmission mechanism in a vacuum pump, an oil contamination free vacuum pump can be provided. 

1. An oil-free fluid machine unit comprising an oil-free fluid machine, a motor connected to one of rotor shafts of the fluid machine, and a mounting base for mounting the fluid machine and the motor, the fluid machine having a rotor casing and two or more lobed rotors accommodated in the rotor casing rotatably to expel gas trapped in pockets formed between the lobes and the rotor casing as the rotors rotate; wherein a pulley is attached to each of said rotor shafts at an end opposite to the motor side end thereof, a belt being looped over pulleys attached to adjacent rotor shafts so that pulleys attached to adjacent rotor shafts are rotated in counter direction to each other; and synchronization gears are attached to the other ends of the rotor shafts respectively, at least one of the synchronization gears being made of plastic material; whereby torque transmission between the rotors is carried out in two ways, via belt driving and via synchronization gear drive.
 2. An oil-free fluid machine unit according to claim 1, wherein an idler pulley is provided to allow pulleys attached to adjacent rotor shafts to be rotated in counter direction to each other by looping a belt over the adjacent pulleys via the idler pulley. 